In dependence of the desired operation direction of the motor on existing control valves, the control valve releases flow paths, from the high-pressure connection to a working line on the one side and from the other working line to the low-pressure connection on the other side. This release, however, occurs in a more or less throttled manner, the height of the throttling resistance depending on the operating stroke (or another corresponding operating movement) of the control valve. In this connection, the compensation valve serves as pressure control valve. In some cases, it is also called pressure balance. It ensures that the pressure over the slide of the control valve is practically always the same. Expediently, the compensation valve exists in the form of a slide, which is acted upon on the one side by a return spring and the load pressure and on the other side by the pressure in a line section between the compensation valve and the control valve.
Usually, such control valves work reliably. Problems occur, when the motor is working with the so-called negative loads. Such negative loads occur, for example, when the motor is activated by an external weight, for example a load hanging in a crane hook. Another example is a vehicle's own weight, which drives on a sloping surface or has to be braked from a certain speed. In this case, the hydraulic system of the control device may tend to oscillate.
It is, therefore, known to arrange a return compensation valve in a working line between the motor and the control valve, which return compensation valve an also be made as a pressure control valve or a pressure balance valve. The return compensation valve ensures that the motor can only be activated, when it is still supplied with pressurised hydraulic fluid.
However, also here oscillations of the system can be observed.
It is therefore an object of this invention to ensure a stable operation in both directions in connection with negative loads in a hydraulic control system.
This and other objects will be apparent to those skilled in the art.